In the pharmaceutical industry, machines are known for filling the bottom shells of capsules with precise doses of at least one pharmaceutical product, and closing the bottom shells with corresponding top shells to obtain respective full capsules as the end product.
Controlling the correct product dosage is traditionally done by weighing the outgoing capsules on electromechanical scales. This system has two main drawbacks. Firstly, the accuracy with which the content of the capsule is weighed is intrinsically limited by weighing the full capsule, and assuming as the tare value the nominal value declared by the maker or a mean batch value, as opposed to the actual weight of each individual empty capsule. Secondly, given the speed limitations of electromechanical scales, only sample control can be done using one scale. For 100% production control, a battery of parallel scales, between which to divide the outgoing capsules, is required.
Considerable improvements to the above method have been made in certain machines of this type manufactured by the Applicant, and wherein weighing is performed at two separate stations, both operating capacitively.
Since, as stated, what is important in machines of this type is the weight of the content of the capsule, the first station weighs the empty capsule (tare), and the second station the full capsule; and, on the basis of the information from the first station, the net weight of the content is determined using appropriate algorithms.
This method, now improved by years of experience, provides for high speed, and therefore 100% production control, and accurate weighing of the actual content. Any capsules containing a product quantity outside the given tolerance range are rejected by an automatic reject system.
At present, these technical improvements are only satisfactory provided sufficient care is taken as regards manufacture of the equipment and performance and processing of the measurements. For example, since the measurements are made on a fast-rotating conveyor wheel, on which the capsules are retained inside cavities, adequate measuring precision calls for ensuring, in particular, precise mechanical tolerances, steady movement of the conveyor wheel, and precise positioning of the capsule inside the respective cavity.
Moreover, this method only provides for controlling the total weight of the product inside capsules or similar. In the case of multicomponent products (products containing a number of components metered successively into the capsule), distinguishing the weights of the individual components involves mechanical complications and providing an additional weighing station downstream from each metering operation.
The present invention therefore provides for improving at least one component forming part of the above capsule filling machines.
On currently used machines, the capsules, as they are being filled, are conveyed by means of a number of bored cylindrical members (seat assemblies), each only housing the bottom shell of a capsule.
The component in question is a “seat assembly” defined herein as “an appropriately shaped, hollow cylindrical member for housing a respective bottom shell”.
When housed inside the seat assembly, the bottom shell is filled with at least one product, which may be in the form of powder, granules, tablets, microtablets, liquid, or gel.
In other words, a respective bottom shell of a capsule is first deposited inside each seat assembly conveyed on the machine, and is then filled in one or a number of successive steps with the desired products; and the full bottom shell is then closed with a top shell to form a corresponding capsule.
It should be pointed out that, in the method currently adopted by the Applicant, a whole empty capsule is first weighed (tare), and is then opened, filled, closed, and weighed again (gross).